System and method for extending neighboring cell search window

ABSTRACT

A system and method for accommodating mobile station synchronization to neighbor cells in a mobile communication system. At least one available frame is utilized as a search window in an uplink data transfer multiframe for receiving neighboring cell synchronization information. At least one transmit time slot in a frame adjacent to the available frame in the uplink data transfer multiframe is surrendered to extend the search window. The neighboring cell synchronization information may then be contiguously received via the extended search window.

RELATED APPLICATIONS

This application is a continuation of prior U.S. application Ser. No.10/356,675, filed Jan. 31, 2003 now U.S. Pat. No. 7,633,927, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates in general to wireless communications, and moreparticularly to a system and method for accommodating mobile stationsynchronization to neighbor cells by providing an extended search windowallowing the mobile station to receive neighbor cells in an efficientmanner.

BACKGROUND OF THE INVENTION

In recent years, the utilization of wireless communication systems forcommunicating telephonically has achieved astonishing popularity.Conventional, voice communications as well as data communications can beeffected telephonically through the use of such wireless communicationsystems.

In a wireless communication system, the communication channel formedbetween a sending and a receiving station is a radio channel, operatingin a portion of the electromagnetic spectrum. A wire line connection isnot required to effectuate the communication of a communication signalbetween the sending and receiving stations. Thus, communication via awireless communication system is possible at locations to whichformation of a wire line connection would be impossible or otherwiseimpractical.

Cellular communication systems have been implemented using variouscommunication schemes. Cellular communication systems have beendeveloped which utilize, for example, FDMA (frequency-division,multiple-access), TDMA (time-division, multiple-access), and CDMA(code-division, multiple-access) techniques, as well as variouscombinations of such techniques. A cellular communication systemincludes network infrastructure including a number of separated basetransceiver stations, formed of fixed-site radio transceivers. Userscommunicate with the infrastructure of a cellular communication networkthrough the use of a radio telephone or other communicator, typicallyreferred to as a mobile station. The mobile station receives downlinksignals on a forward link and transmits uplink signals on a reverselink. In this manner, bidirectional communications are provided betweenthe infrastructure of the cellular communication network and the mobilestation.

For the successful operation of a cellular communication system,synchronization is required between mobile stations and the basetransceiver station. Such synchronization generally comes in two forms,including frequency synchronization and time synchronization of theframes and bits. Frequency synchronization is needed in order to ensurethat the mobile station is synchronized to the carrier frequency of theBTS. Bit and frame synchronization provides adjustment of thepropagation time differences of signals from different mobile stationsso that transmitted “bursts” are received synchronously with the timeslots of the base transceiver station, and so bursts in adjacent timeslots do not overlap. Bit and frame synchronization is also required forthe frame structure due to a higher-level superimposed frame structurefor mapping logical signaling channels onto a physical channel.

Furthermore, when a mobile terminal is operating in a cellularcommunication system, it has to be synchronized to neighboring cells. Inorder to do this, the mobile station attempts to receive synchronizationchannels such as Frequency Correction Channels (FCCH) andSynchronization Channels (SCH) of the neighboring cells at certainintervals. On traffic channels, most of the TDMA frames are used fortransferring data or speech, and limited available frames exist in whichsuch synchronization information may be received. Partial searches canbe performed at different frames to collectively provide the desiredsearch result. However, within any given available frame, the number oftime slots available are also limited, which can further spread out thesearching operation unless enough consecutive times slots can be madeavailable to account for all of the possible places in time that asynchronization signal such as an FCCH can present itself.

With the introduction of higher-level multislot classes, the consecutivetime slots associated with a frame and available for receivingneighboring cell synchronization information becomes prohibitivelylimited. In many cases, there are not enough time slots to cover therange of times in which an FCCH or other synchronization signal can bepresented, and the receipt of FCCH information must carry over tosubsequent frames. This can cause significant delays and adverselyaffect communication throughput.

One prior art manner that addresses this is described in 3GPP TS 05.08,V8.14.0 (2002-04), “3^(rd) Generation Partnership Project; TechnicalSpecification Group GSM/EDGE Radio Access Network; Radio Subsystem LinkControl” (Release 1999), which is incorporated herein in its entirety.This specification indicates that the MS may skip receive operations forneighbor reception purposes. This results in the Rx operation after theidle frame being skipped to provide the requisite time slots forreceiving the FCCH and SCH information. While this may not be necessaryfor unidirectional downlink data transfer (e.g., where sufficientdownlink time slots are allocated), unnecessary breaks in the downlinkand/or uplink data transfer can occur when skipping Rx operations duringunidirectional uplink and bidirectional uplink/downlink data transfer.When using Uplink State Flag (USF), for example, for allocation ofuplink resources, this decreases throughput for both downlink and uplinkdata transfers, since a permission to send uplink data is received in adownlink data block. By skipping Rx operations in the downlinkdirection, this permission to send uplink data may be missed, causingfurther delays. This problem is exacerbated when extended dynamicallocation or USF granularity (or both) are used, since one Rx block mayprovide permission to send multiple Tx blocks.

Accordingly, there is a need in the communications industry for a mannerof receiving neighbor cell synchronization information that minimizesthe impact of widening the associated search window. The presentinvention fulfills these and other needs, and offers other advantagesover the prior art.

SUMMARY

To overcome limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa system, apparatus and method for accommodating mobile stationsynchronization to neighbor cells by providing an extended search windowallowing the mobile station to efficiently receive neighbor cells. Oneor more transmit (Tx) time slots are skipped in an available frameadjacent to a block of time slots available for receiving neighborsynchronization information. In this manner, the search window forreceiving such synchronization information can be expanded, without thenegative consequences associated with prior art synchronizationmethodologies.

In accordance with one embodiment of the invention, a method is providedfor accommodating mobile station synchronization to one or more neighborcells in a mobile communication system. The mobile communication systemincludes base transceiver stations (BTS) each defining a cell, and atleast one mobile station (MS) capable of communicating with at least oneBTS. The method includes utilizing at least one available frame as asearch window in an uplink data transfer multiframe for receivingneighboring cell synchronization information. At least one transmit timeslot in a frame adjacent to the available frame in the uplink datatransfer multiframe is surrendered or “skipped” to extend the searchwindow. The neighboring cell synchronization information is thenreceived in the extended search window.

The following describes various particular embodiments of such a method.For example, in accordance with one particular embodiment of such amethod, surrendering at least one transmit time slot in a frame adjacentto the available frame involves surrendering at least one transmit timeslot in a frame immediately preceding the available frame. In a moreparticular embodiment, this may involve surrendering at least onetransmit time slot from the immediately preceding frame that is closestto the available frame to provide contiguous time slots in the extendedsearch window. In another particular embodiment, the method includesmaintaining an end boundary of the available frame to prevent disturbinga successive frame contiguous with the available frame. Anotherparticular embodiment involves surrendering as many transmit time slotsas necessary to provide the extended search window at a size capable ofaccommodating all of the neighboring cell synchronization information,and in other embodiments receive slots may also be surrendered in theframe adjacent to the available frame and opposite the frame in whichthe at least one transmit time slot was surrendered, in order to furtherextend the search window. In still other particular embodiments, theneighboring cell synchronization information includes a FrequencyCorrection Burst (FB) associated with a Frequency Correction Channel(FCCH) and/or a Synchronization Burst (SB) associated with aSynchronization Channel (SCH). In one particular embodiment, utilizingthe available frame(s) as a search window involves utilizing at leastone defined Idle Frame in the uplink data transfer multiframe. Anotherparticular embodiment involves utilizing any one or more frames in theuplink data transfer multiframe having a plurality of contiguousavailable time slots. In other particular embodiments, the MS isassociated with an MS multislot class that accommodates fewerconsecutive available time slots than are available in the search windowprior to extension, where surrendering the transmit time slot(s) mayinvolve surrendering a number of transmit time slots required toaccommodate the MS multislot class. In one particular embodiment, thismay involve surrendering a number of transmit time slots required toprovide ten consecutive time slots, inclusive of the time necessary forMS radio frequency circuitry to change between a data transfer channeland a synchronization channel. One particular embodiment of such amethod involves at least partially synchronizing the MS with aneighboring cell corresponding to the synchronization informationretrieved via the extended search window, and another embodimentinvolves repeating a search for the neighboring cell synchronizationinformation in a plurality of the available frames to facilitate thereceiving of the neighboring cell synchronization information in theextended search window of at least one of the plurality of availableframes. The synchronization information in one embodiment includes aFrequency Correction Burst (FB) associated with a Frequency CorrectionChannel (FCCH), where the method further includes determining a locationof a Synchronization Channel (SCH) based on a location of the FCCH andreceiving the SCH in an available frame at least one multiframe afterthe FCCH using a timing offset relative to a timing offset of the FCCH.The MS of one embodiment may be of a type in which transmit and receiveoperations are not simultaneously performed, such as a type-1 MS.

In accordance with another embodiment of the invention, a Mobile Station(MS) is provided, where the MS is operable in a wireless network havinga plurality of cells each defined by a Base Transceiver Station (BTS).The MS includes a transceiver to communicate with a plurality ofneighboring BTSs to receive synchronization channels transmitted by theneighboring BTSs. The MS also includes a processing module configured toextend a search window in an uplink data transfer multiframe bysacrificing one or more transmit time slots in a frame of the uplinkdata transfer multiframe adjacent to an available frame where receipt ofsynchronization channels are expected.

In accordance with another embodiment of the invention, a system isprovided for synchronizing communications in a mobile communicationsystem. The system includes a number of cells each defined by a BaseTransceiver Station (BTS), and at least one Mobile Station (MS) forcommunicating with some of the BTSs neighboring the cell in which the MSis currently operating. The MS includes a transceiver to communicatewith the plurality of the neighboring BTSs to receive synchronizationchannels transmitted by the neighboring BTSs, and further includes aprocessing module configured to extend a search window in an uplink datatransfer multiframe by surrendering one or more transmit time slots in aframe of the uplink data transfer multiframe adjacent to an availableframe where receipt of synchronization channels are expected.

In accordance with another embodiment of the invention, acomputer-readable medium is provided which includes stored instructionsthat are executable by a computer system for accommodating mobilestation synchronization to one or more neighbor cells in a mobilecommunication system. The mobile communication system includes basetransceiver stations (BTS) each defining a cell, and at least one mobilestation (MS) capable of communicating with at least one BTS. Theinstructions stored on the computer-readable medium performs stepsincluding utilizing at least one available frame as a search window inan uplink data transfer multiframe for receiving neighboring cellsynchronization information, surrendering at least one transmit timeslot in a frame adjacent to the available frame in the uplink datatransfer multiframe to extend the search window, and receiving theneighboring cell synchronization information in the extended searchwindow.

These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and form a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to accompanying descriptive matter, in whichthere are illustrated and described specific examples of a system,apparatus, and method in accordance with the invention

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in connection with the embodimentsillustrated in the following diagrams.

FIG. 1 illustrates some general aspects of a GSM/GPRS networkenvironment in which the principles of the present invention may beutilized;

FIG. 2 illustrates a representative multiframe hierarchy in which searchwindows may be manipulated in accordance with the present invention;

FIG. 3, which illustrates a representative 52-multiframe relationshipbetween the monitoring MS TCH and a neighbor cell BCCH;

FIG. 4 illustrates an example frame portion for an MSC-6 (3+1)configuration;

FIG. 5 illustrates an example frame portion for an MSC-10 or MSC-11(4+1) configuration;

FIG. 6 illustrates an example frame portion for an MSC-12 (1+4)configuration;

FIG. 7 illustrates an example frame portion for an MSC-12 (1+4)configuration implementing the principles of the present invention;

FIG. 8 is a flow diagram illustrating one embodiment for monitoringneighbor cell synchronization channels using a contiguous time slotsearch window in accordance with the principles of the presentinvention;

FIG. 9 is a flow diagram illustrating an embodiment for monitoringneighbor cell FCCHs using a contiguous time slot search window inaccordance with the principles of the present invention; and

FIG. 10 illustrates a representative mobile station computing systemcapable of carrying out operations in accordance with the invention.

DETAILED DESCRIPTION

In the following description of the exemplary embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration various manners in which the inventionmay be practiced. It is to be understood that other embodiments may beutilized, as structural and operational changes may be made withoutdeparting from the scope of the present invention.

Generally, the present invention provides a system and method foraccommodating mobile station synchronization to neighbor cells byproviding an extended search window allowing the mobile station toreceive neighbor cells in an efficient manner. One or more Tx slots, inthe radio block period adjacent to an idle frame used to receiveneighbor synchronization information, are skipped in order to allowexpansion of the search window. By expanding the search window in thisfashion, other time slot operations such as Rx operations need not bedisrupted which can otherwise cause substantial inefficiencies.

The present invention is applicable in any type of mobile communicationsystems/networks where synchronization to neighboring cells may berequired. In order to facilitate an understanding of the invention, thepresent invention is described in terms of a GSM/GPRS network. However,those skilled in the art will readily appreciate from the descriptionprovided herein that the present invention is equally applicable toanalogous networking environments. FIG. 1 illustrates some generalaspects of a GSM/GPRS network environment 100 in which the principles ofthe present invention may be utilized.

Global System for Mobile communications (GSM) is a digital cellularcommunications system serving as a Public Land Mobile Network (PLMN),where multiple providers may set up mobile networks following the GSMstandard. GSM is capable of providing both voice and data services. AGSM (or analogous) network 100 typically includes components such asMobile Stations (MS) 102, Base Transceiver Stations (BTS) 104, MobileSwitching Center (MSC) 106, etc. A GSM network may be viewed as acollection of various subsystems, including the Radio Subsystem (RSS)which covers radio aspects, Network and Switching Subsystem (NSS) whichmanages functions such as call forwarding, handover and switching, andthe Operation Subsystem (OSS) that manages the network. Various aspectsof the RSS is described in greater detail below.

One or more MSs 102 communicate with the BTS 104 via an air interface.The BTS 104 is a component of a wireless network access infrastructurethat terminates the air interface over which subscriber traffic iscommunicated to and from the MS 102. The Base Station Controller (BSC)108 is a switching module that provides, among other things, handofffunctions, and controls power levels in each BTS 104 of the Base StationSystem (BSS) 110. The BSC 108 controls the interface between the MobileSwitching Center (MSC) 106 and BTS 104 in a GSM mobile wireless network,and thus controls one or more BTSs in the call set-up functions,signaling, and in the use of radio channels.

A General Packet Radio System (GPRS) mobile communications network 112is a packet-switched service for GSM that mirrors the Internet model andenables seamless transition towards 3G (third generation) networks. GPRSthus provides actual packet radio access for mobile GSM andtime-division multiple access (TDMA) users, and is ideal for WirelessApplication Protocol (WAP) services. The BTS 104 also controls theinterface between the Serving GPRS Support Node (SGSN) 114 and the BTS104 in a GPRS network 112. Other BTS, BSC, and SGSN components may alsobe associated with the network system, as depicted by BTS 116 and BSC118 of BSS 120, and SGSN 122.

The MSC module 106 generally includes the MSC, Visiting LocationRegister (VLR) 124, and Home Location Register (HLR) 126. The MSC 106performs a variety of functions, including providing telephony switchingservices and controlling calls between telephone and data systems,switching voice traffic from the wireless network to the landlinenetwork if the call is a mobile-to-landline call, or alternativelyswitching to another MSC if the call is a mobile-to-mobile call. The MSC106 also provides the mobility functions for the network, and serves asthe hub for multiple BTSs. Generally, it is the MSC 106 that providesmobility management for subscribers, in order to register subscribers,and authenticate and authorize services and access for subscribers. InGSM systems, some of the functionality of the MSC 106 may be distributedto the BSC 108, while in other systems such as TDMA systems, the BSC 108functions are often integrated with the MSC 106.

Associated with the MSC 106 is the HLR 126 and VLR 124. The HLR 126 is adatabase that stores information about subscribers in the mobilenetwork, and is maintained by one or more service providers for theirrespective subscribers. The MSC 106 uses the information stored in theHLR 126 to authenticate and register the subscriber by storing permanentsubscriber information including the service profile, the currentlocation of mobile stations, and activity status of the mobile user. TheVLR 124 is a database that may be maintained by the MSC 106 to keeptrack of all the visiting mobile stations within a mobile telephonysystem.

The Serving GPRS Support Nodes (SGSN) 114, 122 serve GPRS mobile bysending or receiving packets via a respective BSS 110, 120, and moreparticularly via the BSC 108, 118 in the context of GSM systems. TheSGSN is responsible for the delivery of data packets to and from themobile stations within its service area, and performs packet routing andtransfer, mobility management, logical link management, authentication,charging functions, etc. In the exemplary GPRS embodiment shown in FIG.1, the location register of the SGSN 114 stores location informationsuch as the current cell and VLR associated with the MS 102, as well asuser profiles such as the International Mobile Subscriber IdentityNumber (IMSI) of all GPRS users registered with this SGSN. Anothernetwork element introduced in the GPRS context is the Gateway GPRSSupport Node (GGSN) 128, which acts as a gateway between the GPRSnetwork 112 and a packet switched public data network, such as datanetwork 130. This gateway 128 allows mobile subscribers to access thepublic data network 130 or specified private IP networks. The connectionbetween the GGSN 128 and the public data network is generally enabledthrough a standard protocol, such as the Internet Protocol (IP).

A variety of other network elements may be employed, such as a ShortMessage Service Center (SMSC) 132. The SMSC 220 is a network elementthrough which short messages (e.g., via Short Messaging Service) may betransmitted, and stored for later transmission in the event that themessage recipient is not reached. The MS 102 may access other services,such as a Multimedia Messaging Service (MMS) provided via the MultimediaMessage Service Center (MMSC) 134.

When an MS 102 is operating in a GSM network such as the GSM networkenvironment 100 of FIG. 1, it has to be synchronized to neighbor cells.In order to do this, the MS 102 attempts to receive certainsynchronization channels of the neighboring cells at certain intervals.A background of the various radio interface channels is provided below.

As previously indicated, the RSS includes components such as MSs, andthe BSS which in turn generally includes a plurality of BTSs and a BSC.The BTS includes radio components such as a transceiver and antenna,while the BSC effects switching between BTSs, manages network resources,etc. The RSS supports a certain number of logical channels that fallwithin two primary categories including the traffic channels (TCH) andthe control channels (CCH). The TCHs are intended to carry data such asencoded speech or user data in circuit switched mode, while Packet DataTCHs (PDTCH) are intended to carry user data in packet switched mode.Multiple full rate channels and multiple packet data TCHs can beallocated to the same MS, which is referred to as multislotconfigurations and multislot packet configurations respectively.

Control channels carry signaling and/or synchronization data. There arecurrently four primary control channel categories in GSM systems,including broadcast, common, dedicated, and CTS control channels. Ofparticular interest with respect to the present invention are thebroadcast control channels. The broadcast channels include FrequencyCorrection Channels (FCCH), Synchronization Channels (SCH), a BroadcastControl Channel (BCCH) as well as Packet BCCH (PBCCH) channels. Aspreviously indicated, when an MS 102 is operating in a GSM network, ithas to be synchronized to neighbor cells. In order to do this, the MS102 attempts to receive FCCH and SCH channels of the neighboring cellsat certain intervals. For example, if the selected cell corresponds tothe cell of BTS 104, the neighboring cells in which FCCH and SCHchannels are to be received may include cells 140, 142, etc. Approximatetiming for a neighbor cell is available when FCCH information has beenreceived successfully. The timing and frequency synchronization can befurther improved by a successful SCH reception.

More particularly, the FCCH carries information for frequency correctionof the MS 102, and is essentially the repeated transmission of Frequencycorrection Bursts (FB). FBs provide a predetermined number of bits ofinformation, such as one hundred forty-two bits of information, as wellas tail and guard periods. This information is transmitted periodicallyfrom the BTS to notify the MSs of frequency adjustments. The informationtransmitted is generally null data, i.e., binary zeros, whichcorresponds to broadcasting an unmodulated carrier—a sine wave. Usingthis information, the MS can identify the channel. The SCH is also usedfor synchronization. Synchronization Bursts (SB) on the SCH transmitinformation which allows the MS to synchronize time-wise with the BTS.SBs are structured such that they include data bits and synchronizationbits, which includes a Base Transceiver Station Identity (BSIC) as wellas a Reduced TDMA Frame Number (RFN). The RFN is essentially the runningnumber of the TDMA frame, which facilitates frame synchronization andallows each MS to be time-synchronized with the BTS. Repeatedbroadcasting of SBs is considered the SCH.

In connection with mapping in time of packet logical channels ontophysical channels, a physical channel allocated to carry packet logicalchannels is referred to as a Packet Data Channel (PDCH). PDCHs aregenerally mapped dynamically onto a 52-frame multiframe. FIG. 2illustrates an example of a multiframe 200, which includes fifty-twoframes (0-51). Each TDMA frame 202 generally includes eight time slots(0-7). The length of a typical FCCH burst (i.e., Frequency CorrectionBurst; FB) is one time slot, such as depicted by time slot 204. Threetail bits 206, 208 and one hundred forty-two data bits 210 are all setto zero in the FB to generate a pure sine wave (PSW) signal. Thisgeneral multiframe structure is used by the monitoring MS TCH/PDCH, aswell as by the neighboring cell BCCH. From the neighboring cell point ofview, an FB is periodically transmitted by the BTS on the BCCH carrier.It is these FCCH or FB bursts that are monitored by an MS whenattempting to receive synchronization channels in an appropriateTCH/PDCH frame 202 from neighbor cells/BTSs.

The FCCH of neighboring cells occurs every 10^(th) or every 11^(th)frame in the 51 TDMA multiframe structure; the last gap before the next51-multiframe start is ten frames. In idle mode, the FCCH can bereceived by a monitoring MS via a continuous search lasting twelveframes. The continuous search is possible in idle mode since most of theTDMA frames are free for these operations. The corresponding SCH is thenlocated in the next TDMA frame having the same timing offset as theFCCH. On traffic channels, most of the TDMA frames are used fortransferring data, fax, speech, etc., and the only available frames inthe 52 TDMA multiframe structure are the so-called “idle frames” whichoccur every 26^(th) TDMA frame. Consequently the MS has to perform thesearch for FCCH in smaller sections. In practice, this means that onepartial FCCH search should last at least nine consecutive time slots inorder to cover all possible places in the time domain in which the FCCHinformation may occur during one TDMA frame. Also, SCH receptionrequires a nine time slot-wide reception window to cover all possibletiming offsets where SCH burst can be received.

This situation is depicted in FIG. 3, which illustrates a representative52-multiframe relationship between the monitoring MS TCH 300 and aneighbor cell BCCH 302. Since the neighbor cell FCCH burst 302 (that themonitoring MS is attempting to receive) is not synchronized with thecell where the monitoring MS is camped, the FCCH burst 302 may be placedanywhere in the time domain. Thus, during one TDMA frame 304 of themonitoring MS data channel (e.g., the “idle frame” from the monitoringMS point of view), the neighbor FCCH burst 302 can begin in any timebetween 0 ms and 4.615 ms in the case of 156.25-bit, 8-slot TDMA frames.The length of the FCCH burst is one time slot (4.615/8 ms), so to coverall possibilities to receive one complete FCCH burst the reception or“search window” should last at least 9 time slots. For example, if thesearch window were only 8 slots wide, only a portion 306 of the FCCHburst 308 of the neighbor cell multiframe 302 would be captured in thesearch window during the X^(TH) partial search. The remaining portion310 of the FCCH burst 312 would be captured in another idle frame duringa subsequent, (X+2)^(TH) partial search 314. Thus, in order to ensurethat the FCCH burst can be captured without such a temporal division, 9time slots should be used to accommodate for all possible times in whichthe FCCH burst can occur.

When higher GPRS, High Speed Circuit Switched Data (HSCSD), or othersimilar services supporting multislot classes are taken into use, thereis a problem of obtaining 9 consecutively available time slots forneighbor FCCH and SCH receive (Rx) operations, since Rx and transmit(Tx) operations occupy most of the time slots. More particularly, apractical implementation would require at least ten consecutivelyavailable time slots, since the MS radio frequency (RF)components/circuitry has to change frequency between the data transferchannel and the channel for the neighboring Rx operation, which requiresa certain switching time for type-1 mobile stations having only a singleRF capability (i.e., no concurrent Rx and Tx operations).

Whether a particular type-1 mobile may experience problems in thisregard depends on the multislot class of the device as well as the Rx/Txslot configuration for that multislot class. Table 1 belowrepresentative examples of particular multislot classes:

TABLE 1 MULTISLOT MAXIMUM NUMBER OF SLOTS CLASS Rx Tx SUM  1 1 1 2  2 21 3 . . .  6 3 2 4 . . . 10 4 2 5 11 4 3 5 12 4 4 5Multislot classes are product-dependent, and determine the maximum datarates that are achievable in both the uplink and downlink. For example,multislot class 6 (MSC-6) can include a sum of four slots per frame fordata transmission, with up to three Rx slots and up to two Tx slots. Theparticular configuration is written in the format “X+Y”, where Xrepresents the quantity of downlink time slots, and Y represents thequantity of uplink time slots. Thus, a multislot class of MSC-6 (3+1)represents multislot class 6, with three downlink (Rx) timeslots and oneuplink (Tx) timeslot per frame.

Current 3GPP specifications (i.e., 3GPP TS 05.08) allow, for somemultislot configurations, Rx operations related to data transfer in thedownlink direction to be skipped to provide the requisite search windowfor neighbor reception purposes. While this may not be necessary forunidirectional downlink data transfer, unnecessary breaks in thedownlink and/or uplink data transfer can occur when skipping Rxoperations during unidirectional uplink and bidirectionaluplink/downlink data transfer. When using an Uplink State Flag (USF) orother analogous indicator for allocating uplink resources, thisdecreases throughput for both downlink and uplink data transfers, sincea permission to send uplink data is received in a downlink data block.More particularly, for each data channel (PDCH in the case of GPRSservice) allocated to the MS, a USF is provided to the MS. Physicalchannels for packet switched transmission are only allocated for aparticular MS when the MS sends or receives data packets, and arereleased after the transmission. Using this “dynamic allocation”principle, multiple MSs can share one physical channel. To preventcollisions, the network indicates which channels are currently availablein the downlink. The USF in the header of downlink packets shows whichMS is allowed to use this channel in the uplink. Thus, by skipping Rxoperations in the downlink direction, this permission to send uplinkdata may be missed, causing further delays. This problem is exacerbatedwhen extended dynamic allocation or USF granularity (or both) are used,since one Rx block may provide permission to send multiple Tx blocks.

FIGS. 4-7 illustrate these multislot class considerations. FIG. 4illustrates an example frame portion 400 for an MSC-6 (3+1)configuration. In this example, a TDMA frame 402 for the uplink includesthree Rx time slots 404 and one Tx time slot 406. An idle frame 408 isused to receive the FCCH burst. For this configuration, eleven timeslots are available, including two time slots 410, 412 to provide the MSwith the appropriate switching time for its RF circuitry, and nine timeslots comprising the FCCH search window 414 for receiving the FCCHinformation (also generally referred to as Neighbor Pure Sine Wave;NPSW). Therefore, with this configuration, there is no particularproblem, as the FCCH search can be performed without having to receiveFCCH information non-contiguously in different idle frames.

FIG. 5 illustrates an example frame portion 500 for an MSC-10 or MSC-11(4+1) configuration. In this example, a TDMA frame 502 for the uplinkincludes four Rx time slots 504 and one Tx time slot 506. An idle frame508 is used to receive the FCCH burst. For this configuration, ten timeslots are available, including two partial time slots 510, 512 toprovide the MS with the appropriate switching time for its RF circuitry.This example assumes that the MS RF circuitry can change frequency inhalf of a time slot period (e.g., 577 μs/2). Otherwise, thisconfiguration would pose a problem, as 9 consecutive available timeslots would not be attainable. However, in the example of FIG. 5, ninetime slots are available for the FCCH search window 514 to receive theFCCH information.

FIG. 6 illustrates an example frame portion 600 for an MSC-12 (1+4)configuration. In this example, a TDMA frame 602 for the uplink includesone Rx time slot 604 and four Tx time slots 606. An idle frame 608 isused to receive the FCCH burst. For this configuration, the originallyavailable search window 610 includes less than nine available timeslots, due to the need for two partial time slots 612, 614 to providethe MS with the appropriate switching time for its RF circuitry. Inorder to accommodate for this, the MS may be allowed to skip Rxoperations after the idle frame for neighbor reception purposes. Thisresults in the Rx operation 616 being skipped to provide the requisitenine time slots for receiving the FCCH information as shown by the newsearch window 618. This decreases throughput for both downlink anduplink data transfers since the USF field is received in a downlink datablock. Where extended dynamic allocation and/or USF granularity areused, one Rx block may provide permission to send multiple Tx blocks,and thus the problem may be exacerbated.

The present invention addresses these problems. Rather than skippingdownlink receive (Rx) operations, the search window is widened byskipping transmit (Tx) operations for uplink data transfer before theidle frame where FCCH or SCH reception is performed. The search windowmay be widened by skipping as many Tx operations as necessary to obtainthe requisite search window width. In this manner, skipping the Rx blockafter the idle frame can be avoided, and the network can thus use thisblock to allocate resources to the MS(s). Thus, the invention has apositive impact on downlink data since no downlink operations need to beskipped. Further, this is particularly beneficial in the context ofextended dynamic allocation and/or USF granularity use, where thenetwork can use the first block to allocate several uplink time slots tothe MS. This way, the receipt of the USF value, for example, in the nextperiod can be effected from all four bursts comprising a GPRS radioblock. As a more particular example, with MSC-12 when extended dynamicallocation and USF granularity is used, this USF may grant permission tosend up to 16 uplink blocks, and it is more significantly more efficientto ensure receipt of the permission for sending these multiple uplinkblocks relative to losing a single uplink block. Besides allocatingresources to the MS, the network can use the first Rx block after theidle frame to send a control or data block which can also containpolling for requesting the mobile stations to send an uplink controlblock.

FIG. 7 illustrates an example frame portion 700 for an MSC-12 (1+4)configuration implementing the principles of the present invention. Inthis example, a TDMA frame 702 for the uplink generally includes one Rxtime slot 704 and four Tx time slots 706, 708, 710, and 712. An idleframe 714 is used to receive the FCCH burst. The originally availablesearch window 716 includes less than nine available time slots, due tothe need for two partial time slots 718, 720 to provide the MS with theappropriate switching time for its RF circuitry. In accordance with thepresent invention, the Rx operation 722 need not be skipped. Rather, thelast Tx slot(s) in the frame 702 prior to the idle frame 714 issurrendered in order to widen the search window as shown by the newsearch window 724. With this widened search window 724, nine contiguoustime slots are available for receiving the FCCH information, without thenegative impact associated with skipping Rx operations 722 after theidle frame 714. It should be noted that MCS 12 is depicted here forpurposes of illustration, but the problem will be significantly morepronounced for other higher multislot classes for type-1 mobile stations(e.g., multislot class 30-45) when extended dynamic allocation orsimilar functionality is used.

When this kind of search is repeated in a plurality of successive idleframes, the neighbor synchronization information shall occur during oneof the extended search windows. For example, in the GSM/GPRSenvironment, this kind of search is repeated in thirteen consecutiveidle frames, the place for the neighbor FCCH burst will occur during oneof the search windows. This is a consequence of different multiframestructures between common control channels (e.g., BCCH) anddedicated/shared channels (e.g., TCH, PDTCH, etc.). After the FCCH hasbeen detected, the location of the SCH is known, and it can be receivedin an idle frame 52 frames after the FCCH using the same timing offsetas detected for the FCCH.

FIG. 8 is a flow diagram illustrating one embodiment for monitoringneighbor cell synchronization channels using a contiguous time slotsearch window in accordance with the principles of the presentinvention. An available frame, such as a TDMA idle frame in a datachannel, is identified 800 as a search window in the uplink datatransfer multiframe. The available frame is identified for receivingneighboring cell synchronization information in the uplink data transfermultiframe. In accordance with the invention, the search window isextended through sacrificing one or more transmit time slots in a frameadjacent to the available frame in the uplink data transfer multiframe,as shown at block 802. For example, in one embodiment of the invention,one or more transmit time slots in the frame immediately preceding theidle frame are skipped in order to provide a number of contiguous timeslots necessary to ensure that the neighboring cell synchronizationinformation will be captured, regardless of when during the extendedsearch window the FCCH is provided by the neighboring cell(s).Alternatively, transmit frames in a successive frame may be skipped,depending on the multislot class configuration utilized. For example, ina multislot class and frame configuration where Tx time slots precede Rxtime slots, transmit time slots in a frame immediately succeeding theidle frame may be skipped. In any case, neighboring cell synchronizationinformation may then be received 804 in the extended search window. Itis noted, however, that this search may be repeated multiple times (suchas in thirteen consecutive idle frames) to ensure a place for theneighbor FCCH to occur during one of the search windows, as describedabove.

FIG. 9 is a flow diagram illustrating an embodiment for monitoringneighbor cell FCCHs using a contiguous time slot search window inaccordance with the principles of the present invention. A TDMA idleframe is identified 900 as a search window in the uplink data transfermultiframe, to receive one or more neighboring cell FCCH bursts. Thesearch window is extended 902 to ten contiguous time slots in theillustrated embodiment. This is due to one particular requirement where9 contiguous time slots are required to ensure receipt of the entireFCCH within an extended search window, and where MS RF circuitry changefrequency in half of a time slot. Therefore, the requisite 9 contiguoustime slots added to two half time slots results in ten time slots forthe extended search window. It will be appreciated by those skilled inthe art from the teachings herein that the search window may be extendedto different lengths, depending on the length of the received FCCH, theMS RF circuitry speed in changing frequency, the multislot classutilized, etc.

In the illustrated embodiment of FIG. 9, the search window is extended902 by skipping a corresponding number of transmit time slots in theframe prior to the idle frame in the uplink data transfer multiframe.For example, where ten contiguous time slots are required (for FCCH plusMS RF frequency change), and nine contiguous time slots are available inthe original search window, then one Tx time slot will be skipped.Again, a different number of Tx time slots may be skipped, depending onthe length of the received FCCH, the MS RF circuitry speed in changingfrequency, the multislot class utilized, etc.

In one embodiment, the search may need to be repeated in a plurality ofsuccessive idle frames, such that the neighbor synchronizationinformation occurs during one of the extended search windows. Forexample, in the GSM/GPRS environment, this kind of search is repeated inthirteen consecutive idle frames, the place for the neighbor FCCH burstwill occur during one of the search windows. This is due to thedifferent multiframe structures between common control channels (e.g.,BCCH) and dedicated/shared channels (e.g., TCH, PDTCH, etc.). In suchcase, it is determined 904 whether the search has been repeated aparticular number of times, such as thirteen times. If not, the nextidle frame 906 is considered, and another search window is identified900. Otherwise, if the search has been repeated the particular number oftimes, the neighboring cell FCCH burst will be received 908 in one ofthe extended search windows of the repeated search.

The present invention may be used with a variety of types of mobilestations, including wireless/cellular telephones, personal digitalassistants (PDAs), or other wireless handsets, as well as portablecomputing devices capable of wireless communication. The mobile stationsutilize computing systems to control and manage the conventional deviceactivity as well as the functionality provided by the present invention.Hardware, firmware, software or a combination thereof may be used toperform the various synchronization search window expansion functionsand operations described herein. An example of a representative mobilestation computing system capable of carrying out operations inaccordance with the invention is illustrated in FIG. 10.

The exemplary mobile station (MS) 1000 suitable for performing thesynchronization search window expansion functions in accordance with thepresent invention may be associated with a number of different types ofwireless devices. The representative MS 1000 includes aprocessing/control unit 1002, such as a microprocessor, reducedinstruction set computer (RISC), or other central processing module. Theprocessing unit 1002 need not be a single device, and may include one ormore processors. For example, the processing unit may include a masterprocessor and associated slave processors coupled to communicate withthe master processor.

The processing unit 1002 controls the basic functions of the MS asdictated by programs available in the program storage/memory 1004. Thus,the processing unit 1002 may execute the search window expansionfunctions associated with the present invention. Alternatively, thesesearch window expansion functions may be implemented in softwareoperable on the Digital Signal Processor 1006, rather than via the MSprocessing unit 1002. The program storage/memory 1004 may include anoperating system and program modules 1008 for carrying out standardfunctions and applications on the MS, as well as functions associatedwith the search window expansion functions of the present invention. Inone embodiment of the invention, the program modules 1008 are stored innon-volatile electrically-erasable, programmable read-only memory(EEPROM), flash ROM, etc. so that the programs are not lost upon powerdown of the MS. The program storage may also include one or more ofother types of read-only memory (ROM) and programmable and/or erasableROM, random access memory (RAM), subscriber interface module (SIM),wireless interface module (WIM), smart card, or other removable memorydevice, etc. The relevant software for carrying out MS operations inaccordance with the present invention may also be transmitted to the MS1000 via data signals, such as being downloaded electronically via oneor more networks, such as the Internet and an intermediate wirelessnetwork(s).

The processor 1002 and/or DSP 1006, under the direction of one or moreprogram modules 1008, performs search window expansion functionsassociated with the present invention. For example, in one embodiment ofthe invention, one or more transmit operations are skipped in the frameimmediately preceding the idle frame. The processor 1002 and/or DSP 1006perform such skipping functions under the control of one or moresoftware/firmware programs associated with program modules 1008. Whilesuch functions can alternatively be performed using discrete hardware,these functions are performed using the processor 1002 and/or DSP 1006in the illustrated embodiment.

For performing other standard MS functions, the processor 1002 is alsocoupled to user-interface 1010 elements associated with the MS 1000. Theuser-interface 1010 of the MS may include, for example, a display 1012such as a liquid crystal display, a keypad 1014, speaker 1016, andmicrophone 1018. These and other user-interface components are coupledto the processor 1002 as is known in the art. The keypad 1014 includesalpha-numeric keys for performing a variety of functions, includingdialing numbers and executing operations assigned to one or more keys.Other user-interface mechanisms may be employed, such as voice commands,switches, touch pad/screen, graphical user interface using a pointingdevice, trackball, joystick, or any other user interface mechanism. Thekeypad 1014 will be different depending on the type of MS 1000 utilized.

The MS 1000 also includes conventional circuitry for performing wirelesstransmissions. The DSP 1006 may be employed to perform a variety offunctions, including analog-to-digital (A/D) conversion,digital-to-analog (D/A) conversion, speech coding/decoding,encryption/decryption, error detection and correction, bit streamtranslation, filtering, etc., as well as the functions associated withthe present invention. The transceiver 1020, generally coupled to anantenna 1022, transmits the outgoing radio signals 1024 and receives theincoming radio signals 1026 associated with the MS.

The MS 1000 of FIG. 10 is provided as a representative example of amobile device in which the principles of the present invention may beapplied. From the description provided herein, those skilled in the artwill appreciate that the present invention is equally applicable in avariety of other currently known and future mobile devices.

Using the description provided herein, the invention may be implementedas a machine, process, or article of manufacture by using standardprogramming and/or engineering techniques to produce programmingsoftware, firmware, hardware or any combination thereof. Any resultingprogram(s), having computer-readable program code, may be embodied onone or more computer-usable media, such as disks, optical disks,removable memory devices, semiconductor memories such as RAM, ROM,PROMS, etc. Articles of manufacture encompassing code to carry outfunctions associated with the present invention are intended toencompass a computer program that exists permanently or temporarily onany computer-usable medium or in any transmitting medium which transmitssuch a program. Transmitting mediums include, but are not limited to,transmissions via wireless/radio wave communication networks, theInternet, intranets, telephone/modem-based network communication,hard-wired/cabled communication network, satellite communication, andother stationary or mobile network systems/communication links. From thedescription provided herein, those skilled in the art are readily ableto combine software created as described with appropriate generalpurpose or special purpose computer hardware to create a synchronizationsearch window expansion system and method in accordance with the presentinvention.

The foregoing description of the exemplary embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. For example, while the present inventionis largely described in terms of GSM/GPRS, the present invention isequally applicable to other networks and services having similarcharacteristics as it pertains to the receipt of synchronizationinformation from neighboring cells, and those skilled in the art willappreciate from the description provided herein that the principles ofthe present invention are equally applicable to such other networksand/or services. Thus, it is intended that the scope of the invention belimited not with this detailed description, but rather determined fromthe claims appended hereto.

1. An apparatus comprising: a processor configured to use at least oneavailable frame as a search window in an uplink data transfer multiframefor receiving neighboring cell synchronization information, and toextend the search window by skipping one or both of at least onetransmit time slot in one of the frames adjacent to the available framein the uplink data transfer multiframe and at least one receive timeslot in one of the frames adjacent to the available frame in the uplinkdata transfer multiframe; and a receiver configured to receive theneighboring cell synchronization information in the extended searchwindow from neighboring base transceiver stations.
 2. The apparatus ofclaim 1, wherein the processor comprises a processor device operatingunder the direction of one or more program modules having instructionsto direct the processor to skip the one or more transmit time slots inthe frame adjacent to the available frame.
 3. The apparatus of claim 1,wherein the processor comprises a digital signal processor operatingunder the direction of one or more program modules having instructionsto direct the digital signal processor to skip the one or more transmittime slots in the frame adjacent to the available frame.
 4. Theapparatus of claim 1, wherein the available frame comprises a definedIdle Frame in the uplink data transfer multiframe.
 5. The apparatus ofclaim 4, wherein the processor is configured to extend the search windowby skipping at least one transmit time slot in the frame immediatelypreceding the Idle Frame.
 6. The apparatus of claim 1, where in theprocessor is further configured to skip as many transmit slots asnecessary to provide the extended search window with a size capable ofaccommodating all of the neighboring cell synchronization information.7. The apparatus of claim 1, wherein the processor is configured to skipboth the transmit time slot and the receive time slot, wherein the atleast one receive time slot is skipped in the frame adjacent to theavailable frame and opposite the frame in which the at least onetransmit time slot is skipped.
 8. The apparatus of claim 7, wherein theavailable frame comprises a defined Idle Frame in the uplink datatransfer multiframe and the processor is further configured to extendthe search window by skipping at least one transmit time slot in theframe immediately preceding the Idle Frame and skipping at least onereceive time slot in the frame immediately subsequent the Idle Frame. 9.The apparatus of claim 7, wherein the processor is further configured toskip as many transmit and receive time slots as necessary to provide theextended search window with a size capable of accommodating all of theneighboring cell synchronization information.
 10. The apparatus of claim1, wherein the processor is further configured to use any one or moreframes in the uplink data transfer multiframe having a plurality ofcontiguous available time slots.
 11. A system comprising: (a) aplurality of cells each defined by a base transceiver station; (b) atleast one mobile station for communicating with a plurality of the basetransceiver stations neighboring the cell in which the mobile station iscurrently operating, wherein the mobile station comprises: (i) aprocessor configured to use at least one available frame as a searchwindow in an uplink data transfer multiframe for receiving neighboringcell synchronization information, and to extend the search window byskipping at least one transmit time slot in one of the frames adjacentto the available frame in the uplink data transfer multiframe orskipping at least one receive time slot in one of the frames adjacent tothe available frame in the uplink data transfer multiframe; and (ii) areceiver configured to receive the neighboring cell synchronizationinformation in the extended search window from neighboring basetransceiver stations.
 12. The system of claim 11, wherein the system isoperable in a GSM network.
 13. The system of claim 11, wherein theavailable frame comprises a defined Idle Frame in the uplink datatransfer multiframe.
 14. The system of claim 13, wherein the processoris further configured to extend the search window by skipping at leastone transmit time slot in the frame immediately preceding the definedIdle Frame.
 15. The system of claim 11, wherein the mobile station isassociated with a mobile station multislot class which accommodatesfewer consecutive available time slots than are available in the searchwindow prior to extension.
 16. The system of claim 11, wherein themobile station comprises a mobile station type where transmit andreceive operations are not simultaneously performed.
 17. A method,comprising: utilizing, via a processor, at least one available frame asa search window in an uplink data transfer multiframe for receivingneighboring cell synchronization information; skipping, via theprocessor, one or both of at least one transmit time slot and at leastone receive time slot in respective frames adjacent to the availableframe in the uplink data transfer multiframe to extend the searchwindow; and receiving, via a receiver, the neighboring cellsynchronization information in the extended search window.
 18. Themethod of claim 17, wherein skipping at least one transmit time slot ina frame adjacent to the available frame comprises skipping at least onetransmit time slot in a frame immediately preceding the available frame.19. The method of claim 18, wherein skipping at least one receive timeslot in a frame adjacent to the available frame comprises skipping atleast one receive time slot in a frame immediately following theavailable frame.
 20. The method of claim 17, wherein skipping both thetransmit time slot and the receive time slot comprises skipping as manytransmit and receive time slots as necessary to provide the extendedsearch window at a size capable of accommodating all of the neighboringcell synchronization information.
 21. An apparatus comprising: aprocessor configured to use at least one available frame as a searchwindow in an uplink data transfer multiframe for receiving neighboringcell synchronization information, and to extend the search window byskipping at least one transmit time slot in one of the frames adjacentto the available frame in the uplink data transfer multiframe; and areceiver configured to receive the neighboring cell synchronizationinformation in the extended search window from neighboring basetransceiver stations.